Ink jet array printers employing one or more rows of ink jet printing guns and serving as pattern printers are described, for example, in United Kingdom Pat. Nos. 1,354,890 and 1,432,366 though when employing one row only of ink jet printing guns, they may be used for character or facsimile printing.
The printing apparatus described in the specifications referred to is adapted to print by depositing small drops of ink in accordance with printing information on a surface to be printed during continuous movement relatively to the apparatus of the surface and comprises one or several rows of ink jet printing guns, each gun having means for supplying printing ink under pressure to an orifice, means for forming regularly spaced drops in the ink stream issuing from the orifice, charge electrode means for charging the drops, means for applying to the charge electrode means, under the control of the printing information, a periodic printing voltage waveform whose period is sufficient to span the formation of a series, hereinafter referred to as a "raster" of consecutively formed drops, drop deflection means for providing transverse to the direction of relative movement of the apparatus and the printing surface a substantially constant electrostatic field through which the drops pass towards the printing surface thereby to deflect electrically charged drops transversely to said direction of relative movement to an extent dependent upon the charge levels on the drops and drop intercepting means for collecting drops other than those drops charged for printing on the printing surface, the drops charged for printing in the printing guns during each period of the voltage waveform being deposited in respective line sections formed by contiguous drops which sections together present a printed line transversely of the direction of relative movement, the printed lines being formed in contiguity successively at the frequency of the voltage waveform applied to the charge electrode means.
An ink jet printer as distinct from an ink jet array printer would possess a single printing gun of the structure described for the array printer and the line section of drops deposited by the gun in successive periods of the voltage waveform would constitute the contiguous print line.
Preferably start pulses are generated in the printer at intervals which correspond to the separation between successive printed lines during the motion of the printing surface, and the said voltage waveform is applied in the charge electrode means to the next formed drop following the start pulses and to the succeeding drops during the period thereof in accordance with United Kingdom Pat. No. 1,479,963. In this manner line sections are deposited at selected constant spacing on the printing surface, although the velocity of the surface is variable, and although the intervals which separate the start of the periods of the voltage waveform are also variable. Preferably also the series of voltage levels in the voltage waveform, which as specified spans the formation of a raster of drops formed in each printing gun, comprises a sequence of voltage levels generated in time order which is different from the sequence in order of magnitude, and the consecutive generation of high level voltages in the waveform for adjacent drops is as far as practical avoided in accordance with United Kingdom Pat. No. 1,491,234. Further the voltage levels generated in the voltage waveforms are modified in accordance with United Kingdom Pat. No. 1,533,659 to compensate in the location on the printing surface to which each drop is deflected for the effect thereon of adjacent drops in the event that said adjacent drops are inhibited from printing in accordance with the controlling printing information.